This invention relates to a tubular substance made by winding prepreg provided by impregnating reinforcing fibers aligned or oriented mainly in one direction with thermosetting resin and pressurizing and heating it, and a manufacturing method therefor. Therefore, it can be used for rod pipes of fishing rods, shafts of golf clubs, etc.
Fishing rods need to be lightweight because they are held for long hours and from the viewpoint of improvement in operability and further need to be improved in strength because they receive a large bend force of strong pulling of fish, etc. Golf clubs also need to have light and highly strong nature. Thus, fishing rods and shafts of golf clubs need to satisfy compatibility of antithetic properties of lightweight and high strength. Therefore, hitherto, lightweight and strong tubular substances have been made by impregnating highly strong and lightweight fibers such as carbon fibers with synthetic resin such as epoxy resin for forming prepreg and winding, pressurizing, and heating the prepreg.
In this case, the fact that the weight percentage of resin in the prepreg generally is 35% to 40% is disclosed in Japanese Patent Publication No.Hei 2-44492. The Publication specifies the relationship between the resin impregnation amount of the first prepreg of the innermost layer of a rod pipe and that of the second prepreg for the main layer of an outer layer from the viewpoints of conformability with the mandrel and coherency of the layers, wherein the fact that the resin impregnation amount of the prepreg of the innermost layer is 50% or less and that of the outer layer is 30% or less is disclosed.
However, the weight increases because the resin amount is large as a whole. Further, because the above-disclosed resin amount is too much with respect to fibers, the formation of a resin layer or resin pool (portion with no or few fibers) where delamination or crack easily occurs is observed from photomicrographs. A resin flow occurs during molding, and thus fibers also move easily in association with the resin flow to meander or lean to one side, whereby lowering of strength or unintentional bending easily occurs.
Particularly, if the resin amount of the prepreg for the main layer exceeds about 25 wt %, when the prepreg is wound and thereafter tightened with tape and heat-molded, circumferential shift of the prepreg material occurs during the molding depending on the tightening condition and molding failure often occurs. However, if prepreg impregnated evenly with a small amount of resin is used, coherency on boundaries of wound layers worsens and voids occur on the boundaries. Particularly on the prepreg-wound layer boundaries of fibers oriented in the length direction of the mandrel, the voids easily occur continuously in the length direction, causing the strength to lower due to delamination.
Japanese Utility Model Laid-Open Publication No.Hei 6-7923 discloses the fact that heating and molding in a state in which a resin flow from an inner layer to surface layer is suppressed is a point to be considered. On the other hand, this publication also discloses the fact that an inner reinforcement layer contains a larger resin impregnation amount than the main layer for conformity with a mandrel and that an outer reinforcement layer contains a larger resin impregnation amount than the main layer for discharging air pools.
However, if the resin percentages of the reinforcement layers are set larger than that of the main layer for conformity with the mandrel and for pushing out air pools of the outer reinforcement layer, the resin flow from the inner layer to the outer layer is not completely suppressed. Therefore, it is desired that the layers have the same resin percentage.
The conformity with the mandrel may be achieved, for example, by adjusting the molding temperature and pressurization force instead of setting the large amount of resin. Air pools can be pushed out by another method instead of setting the large amount of resin for preventing air pools from being produced at prepreg molding. However, the lightweight of the molded rod pipe and improvement in the specific rigidity can be accomplished only by adjusting the resin amount.